Proton and Deuteron Magnetic Resonance and Double Resonance Studies of Hydrogenated Amorphous Silicon

High quality plasma-deposited thin films of a -Si:H and a-Si:H,D(B,P) are investigated between 4.2K and 400K using NMR. A partially deuterated a-Si(H,D) sample H541 provides an unique opportunity to study molecular HD, D_2 and also silicon bonded deuterons through cross-polarization. Proton NMR reveals that there is a weakly-loaded EQQ-quenched orthohydrogen component that is physisorbed on internal surfaces and a linear relation exists between the hydrogen content and the ratio of the number density of orthohydrogen relaxation centers and the number density of protons. Deuteron NMR has revealed a weakly-loaded paradeuterium component. The fit to the Fedders model for relaxation of isolated orthohydrogen or paradeuterium and the Van Kranendonk-Walker molecular rates suggest that the characteristic temperature may range up to 80 K. The DMR spectrum consists principally of a quadrupolar powder doublet and a broad central component. A combined density matrix calculation and double resonance experiments have provided a better understanding of deuteron spin dynamics, particularly of deuteron in molecular HD. HD multiple echoes are associated with HD molecules physisorbed on internal surfaces and reflect a distribution of {bover a}. At 20, 27 and 40 K, the spin lattice relaxation of deuterons via cross relaxation to protons is negligible in a-Si(H,D) samples. The relaxation of deuterons in HD molecules is found to proceed principally via spin diffusion to paradeuterium relaxation centers. A modified Jeener-Broekaert sequence was developed. It suppresses dipolar order, improves the signal to noise ratio of HD multiple echoes and transfers the HD multiple echo signal from the t = tau echo to the auxiliary echoes. Less than 23% of the broad central component is associated with weakly bound deuterium. Most of the central signals arise from molecular HD and paradeuterium. A Jeener-Broekaert pulse sequence with cross-polarization was developed for the study of the decay of quadrupolar order. It reduced the experiment time to 4% of that required for a regular Jeener-Broekaert pulse sequence and allowed a temperature dependent study of the quadrupolar relaxation time of the broad central component and the quadrupolar doublet.